Brush type electric motors generate electromagnetic radiation during commutation. Electromagnetic radiation causes electromagnetic interference (EMI) in nearby electronic devices. Typically, a motor housing is grounded to decrease the EMI transmitted to other electric devices and filters are added to suppress the EMI. A typical grounding connection structure of a motor, as shown in FIG. 1, includes electrical components mounted on one side of the terminal holder. The components include two inductors L1′, L2′ and two grounding resistors R1′, R2′ respectively connected to the inductors L1′, L2′ by a corresponding terminal One lead of the grounding resistor R1′ and one lead of the grounding resistor R2′ are connected with the terminals. The other lead of the grounding resistor R1′ and the other lead of the grounding resistor R2′ extend into slots in a periphery of the terminal holder and extend to the other side of the terminal holder. During assembly, the terminal holder is first arranged in the motor housing, and then the end cap is connected to the housing. After that, the other lead of the grounding resistor R1′ and the other lead of the grounding resistor R2′ rest on the inner surface of the end cap and electrically connect to the end cap to achieve the ground connection. FIG. 1 shows a schematic circuit diagram of the grounding connection. The inductors L1′, L2′ are connected between the positive and negative brushes and the motor terminals, and the motor is grounded via the grounding resistors R1′, R2′.
The method of connecting the resistors to the motor housing by pinching the leads between the terminal holder and the housing and/or between the motor housing and the end cap results in deformation of the housing and/or the end cap with undesirable effects on the motor especially as designers try to increase the motor efficiency of the motor and to increase the power density of the motor. Also, due to relative movement between the parts, the electrical connection can become unstable in high temperature and high vibration environments.
Also, manufacturing tolerance of the housing, the terminal holder and the end cap may lead to an unreliable electric connection and a failure of the ground connection of the motor.